Southern of mouse tail

We have found that certain enzymes do not work well for Southern
blotting of mouse tail DNA, although the are OK for Southern of ES cell
DNA.
Examples: XbaI, HindIII. Other enzymes such as BamHI are Ok also for
tail DNA. We have used both a protocol with UREA - proteinase K - phenol
chloroform, as well as a protocol in which the urea step was omitted.
Are certain enzymes more sensitive to inhibitory factors?
Could we use a better protocol go get rid of the inhibitory influence?
Columns? Dialysis?
Thank you
J-O Jansson